Various printing technologies are used to print images onto a print medium such as paper. One type of printing technology is laser printing. Laser printing works by passing a print medium along a charged photoconductive roller. As the photoconductive roller rotates, a laser is used to remove charge at certain locations along the roller. These locations represent the image to be placed onto the print medium. The locations with removed charge are then rolled passed a development roller having a toner disposed thereon. The toner is given the same charge as the photoconductive roller. The locations where the charge was removed by the laser will pick up the charged toner particles. The toner is then pressed onto the print medium as it passes along the photoconductive roller.
One type of toner is a liquid toner. One example of a liquid toner is Hewlett-Packard Co. ElectroInk® liquid toner. More detail on liquid toners will be given below. In order to give the liquid toners within the liquid toner tanks the appropriate charge, a charge director is injected into the liquid toner tanks. A system of pumps and manifolds are generally used to move the charge director from a charge director tank to the liquid toner tanks. Various inconsistencies between different colors and different types of liquid toners cause the liquid toners to respond differently to the same amount of charge director. This can cause inconsistency between the charge density of the liquid toners over time. This inconsistency in charge density leads to an inconsistency in the amount of liquid toner which is picked up by the photoconductive roller. The inconsistency in liquid toner picked up by the photoconductive roller then leads to a color inconsistency in the image printed onto the print medium.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.